Until/if they buff Voidwalker, this solution should get you through in the meantime.
The early Demonology Tree in WoW: Forever is very strong. Your Voidwalker will benefit from it far more than even a Hunter pet will benefit from Beast Mastery in the early levels.
Go into the tree and get improved health funnel 2/2, Unholy power 3/5, then Demonic Energies which passively heals your pet as you do damage in combat 2/2, this being the essential one. After that get Fel Vitality 3/3 and Improved Voidwalker 3/3.
With those talents alone, which will take you until only level 22 to reach, your Voidwalker will be stronger than a Beast Mastery Hunter’s pet of the same level. The passive healing from Demonic Energies is insanely strong for leveling.
After this you want to go into Affliction and get Suppression 5/5 and then Soul Harvest 2/2.
These talents will boost your leveling progress significantly and keep your pet alive and powerful enough to help you through almost any level appropriate situation you find yourself in whether it’s accidentally pulling 2-3 mobs, soloing an elite quest, etc.